query on 4.5" newt...

hi all.

i have a 4.5" celestron scope, and it's been banged about quite a lot
(it lived in the car trunk for a couple of thousand miles of fairly bad
roads), and i had the opportunity to set it up again yesterday.

this is what i observed: stars are point-sources with *no* coma at all,
nor is there any sort of color fringing around them. and saturn's an
amazingly real jewel too. but it was with jupiter that i was a little
disappointed. with a 20mm ep it shows up as a very good disc (with 4
jovian satellites), but the disc is not sharp at all, and i could
detect some color fringes too... red on top and blue at bottom. using a
10mm ep only made the matter worse, in addition to not allowing me to
focus properly (moons were visible with the 10mm too, and they were
point sources again).

one point to note is that while saturn was pretty high up (almost near
the zenith), jupiter had risen only for an hour or so and there was a
large amount of light pollution too... but i could see 4 moons very
clearly.

since i bought this 1.5+yrs ago, i've never collimated it even once, as
i never observed any sort of coma around stars. plus, i believe
celestron supplied plossl eyepieces with this model (114eq firstscope
short).

the fact that point sources are *very* clear means that it doesn't needcollimation, despite rolling around my car's trunk... is this
assumption correct? if this is the case, how come jupiter didn't
resolve well? is this only due to its low position or is there
something i'm entirely missing?

query on 4.5" newt...

alternatively, my mind's a blank wrote:

Those fringers are telltale signs of atmospheric dispersion, which is
to be expected when Jupiter is low in the sky. The fact that you can
see the four Galilean satellites is not very indicative, since they
are as good as point sources to a 4-1/2-inch telescope and you should
see them as well as you can see any star.

Atmospheric dispersion means, in a sense, that the color registration
of your view is not very good, and therefore the details will get all
washed out. This is especially deleterious with Jupiter, which has
lots of detail to see when conditions are right.

Is this an f/8 scope? If so, the focal length is 900 mm and your 10 mmeyepiece "only" yields 90x. That's not very high power, and you won't
see the effects of miscollimation unless it's pretty poor. Those
effects are, unfortunately, most easily seen on Jupiter as a loss in
detail. But it could just be dispersion. Get up early in the morning
and try Jupiter again, and you'll have a better idea as to what's going
on.